It is known for an extruded plastic tube to be cut to length in a portion-wise manner and for plastic bottles to be blown therefrom. This then involves what are referred to as EBM bottles (Extrusion Blow Molding). The plastic material of such known bottles is HDPE (High Density Polyethylene). Those plastic bottles are closed by the dome which is formed from the tube portion in the blowing operation (the dome is also referred to as the “blowing tulip”) being fused closed and left on the bottle, in the air-tightly fused condition. When that fusing operation is effected using sterile air or in an atmosphere with a low level of germs, the internal space of the respective plastic bottle is germ-free or has a low level of germs therein, and remains in that condition until the dome is removed. The operation of fusing the bottle dome shut can be effected for example by a procedure whereby the walls of the dome are pressed against each other by two pressing jaws which are moved towards each other, and thereby the walls are heat-sealed to each other as long as the plastic material of the dome walls is still sufficiently hot. Such plastic bottles can be pre-produced and stored until they are filled, without the risk of contamination of the interior of the bottle. In the known opening process, the bottle, before being filled in the filling machine, is sterilized on the outside, dried, and then the dome on the bottle is cut off in a clean room environment.
In the known device, the operation of cutting off the bottle dome is effected by a cutting blade which is moved transversely with respect to the direction of movement of the blowing dome, laterally to same, and the bottle is held in the region of the main body portion of the bottle, with the disadvantage that the cut can go astray because the spacing between the holding action at the main body portion of the bottle and the cutting location at the bottle dome is comparatively large and permits twisting in the course of the cutting movement. Waste particles which are produced in the cutting operation are sucked away or blown away by means of a flow of sterile compressed air, whereby valuable sterile air is continuously lost. A cut cannot be precisely guided when dealing with larger bottles.
The attempt has therefore already been made to hold a blade pneumatically movably on a cutting head in such a way that, after the plastic bottle has been clamped fast in its lower region, the blade is guided around the dome region. In this case also the cut cannot be precisely initiated at the desired location because the bottle is not accurately centered and the torque occurring due to the rotating blade at the neck and dome of the bottle is not compensated and properly accommodated. In addition the blade moves under the effect of friction over the laterally projecting spray-over skin on the dome, which skin can be torn off and drop into the interior of the bottle. A further disadvantage is that holding the bottle in its lower region means that it is only ever possible to process one type of bottle, and for cutting off the dome on another type of bottle, the machine has to be converted beforehand. With an expensive construction, the pneumatically actuated cutting blade is pushed a distance into the central passage of the cutting head and the waste particles and pieces which are cut off are sucked away through the central passage, with the disadvantage of continuous losses of sterile air. The cutting head and the blade drive require expensive rotatable structures and pneumatically sealed passages.